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Remove explicit backing field generated Relay Commands when possible #1162

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4793e28
WIP Use implicit field with fieldkeyword when possible for RelayComma…
Avid29 Feb 7, 2026
42eb6be
Changed GetSyntax to use a ImmutableArrayBuilder for RelayCommandGene…
Avid29 Feb 7, 2026
6e48ed0
Fixed field token definitions
Avid29 Feb 7, 2026
314633d
Added conditional compilation check for backing fields assertions in …
Avid29 Feb 7, 2026
fbb227c
WIP Use implicit field with fieldkeyword when possible for RelayComma…
Avid29 Feb 7, 2026
3699f11
Changed GetSyntax to use a ImmutableArrayBuilder for RelayCommandGene…
Avid29 Feb 7, 2026
6a23140
Fixed field token definitions
Avid29 Feb 7, 2026
4a2c060
Added conditional compilation check for backing fields assertions in …
Avid29 Feb 7, 2026
7bb8a81
Merge branch 'main' into relay-command-sg_field-keywords
Avid29 Mar 30, 2026
172f43a
Added using to dispose member declarations builder
Avid29 Apr 12, 2026
de845d7
Merge
Avid29 Apr 12, 2026
a3e4d89
Added RelayCommandAttribute named optional parameter to force backing…
Avid29 Apr 12, 2026
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2 changes: 1 addition & 1 deletion ...tics/Analyzers/WinRTRelayCommandIsNotGeneratedBindableCustomPropertyCompatibleAnalyzer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,7 @@ public override void Initialize(AnalysisContext context)
return;
}

(_, string propertyName) = RelayCommandGenerator.Execute.GetGeneratedFieldAndPropertyNames(methodSymbol);
(_, string propertyName) = RelayCommandGenerator.Execute.GetGeneratedFieldAndPropertyNames(methodSymbol, context.Compilation);

if (DoesGeneratedBindableCustomPropertyAttributeIncludePropertyName(generatedBindableCustomPropertyAttribute, propertyName))
{
Expand Down
4 changes: 2 additions & 2 deletions src/CommunityToolkit.Mvvm.SourceGenerators/Input/Models/CommandInfo.cs
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Expand Up @@ -11,7 +11,7 @@ namespace CommunityToolkit.Mvvm.SourceGenerators.Input.Models;
/// A model with gathered info on a given command method.
/// </summary>
/// <param name="MethodName">The name of the target method.</param>
/// <param name="FieldName">The resulting field name for the generated command.</param>
/// <param name="FieldName">The resulting field name for the generated command, or null if the <see langword="field"/> is available.</param>
/// <param name="PropertyName">The resulting property name for the generated command.</param>
/// <param name="CommandInterfaceType">The command interface type name.</param>
/// <param name="CommandClassType">The command class type name.</param>
Expand All @@ -26,7 +26,7 @@ namespace CommunityToolkit.Mvvm.SourceGenerators.Input.Models;
/// <param name="ForwardedAttributes">The sequence of forwarded attributes for the generated members.</param>
internal sealed record CommandInfo(
string MethodName,
string FieldName,
string? FieldName,
string PropertyName,
string CommandInterfaceType,
string CommandClassType,
Expand Down
123 changes: 80 additions & 43 deletions src/CommunityToolkit.Mvvm.SourceGenerators/Input/RelayCommandGenerator.Execute.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,7 @@ public static bool TryGetInfo(
token.ThrowIfCancellationRequested();

// Get the command field and property names
(string fieldName, string propertyName) = GetGeneratedFieldAndPropertyNames(methodSymbol);
(string? fieldName, string propertyName) = GetGeneratedFieldAndPropertyNames(methodSymbol, semanticModel.Compilation);

token.ThrowIfCancellationRequested();

Expand Down Expand Up @@ -207,25 +207,33 @@ public static ImmutableArray<MemberDeclarationSyntax> GetSyntax(CommandInfo comm
.Select(static a => AttributeList(SingletonSeparatedList(a.GetSyntax())))
.ToArray();

// Construct the generated field as follows:
//
// /// <summary>The backing field for <see cref="<COMMAND_PROPERTY_NAME>"/></summary>
// [global::System.CodeDom.Compiler.GeneratedCode("...", "...")]
// <FORWARDED_ATTRIBUTES>
// private <COMMAND_TYPE>? <COMMAND_FIELD_NAME>;
FieldDeclarationSyntax fieldDeclaration =
FieldDeclaration(
VariableDeclaration(NullableType(IdentifierName(commandClassTypeName)))
.AddVariables(VariableDeclarator(Identifier(commandInfo.FieldName))))
.AddModifiers(Token(SyntaxKind.PrivateKeyword))
.AddAttributeLists(
AttributeList(SingletonSeparatedList(
Attribute(IdentifierName("global::System.CodeDom.Compiler.GeneratedCode"))
.AddArgumentListArguments(
AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(RelayCommandGenerator).FullName))),
AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(RelayCommandGenerator).Assembly.GetName().Version.ToString()))))))
.WithOpenBracketToken(Token(TriviaList(Comment($"/// <summary>The backing field for <see cref=\"{commandInfo.PropertyName}\"/>.</summary>")), SyntaxKind.OpenBracketToken, TriviaList())))
.AddAttributeLists(forwardedFieldAttributes);
ImmutableArrayBuilder<MemberDeclarationSyntax> declarations = ImmutableArrayBuilder<MemberDeclarationSyntax>.Rent();
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@huguesv huguesv Apr 11, 2026

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Based on other usage of ImmutableArrayBuilder.Rent, it's meant to be disposed.
https://github.com/search?q=repo%3ACommunityToolkit%2Fdotnet%20ImmutableArrayBuilder&type=code

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@Avid29 Avid29 Apr 12, 2026

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Nice catch. I thought that the ToImmutable call at the end of the function disposed the builder, but upon further investigation, I was wrong. I'll add a using declaration, so dispose is called at the end of the scope.


// Declare a backing field if needed
if (commandInfo.FieldName is not null)
{
// Construct the generated field as follows:
//
// /// <summary>The backing field for <see cref="<COMMAND_PROPERTY_NAME>"/></summary>
// [global::System.CodeDom.Compiler.GeneratedCode("...", "...")]
// <FORWARDED_ATTRIBUTES>
// private <COMMAND_TYPE>? <COMMAND_FIELD_NAME>;
FieldDeclarationSyntax fieldDeclaration =
FieldDeclaration(
VariableDeclaration(NullableType(IdentifierName(commandClassTypeName)))
.AddVariables(VariableDeclarator(Identifier(commandInfo.FieldName))))
.AddModifiers(Token(SyntaxKind.PrivateKeyword))
.AddAttributeLists(
AttributeList(SingletonSeparatedList(
Attribute(IdentifierName("global::System.CodeDom.Compiler.GeneratedCode"))
.AddArgumentListArguments(
AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(RelayCommandGenerator).FullName))),
AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(RelayCommandGenerator).Assembly.GetName().Version.ToString()))))))
.WithOpenBracketToken(Token(TriviaList(Comment($"/// <summary>The backing field for <see cref=\"{commandInfo.PropertyName}\"/>.</summary>")), SyntaxKind.OpenBracketToken, TriviaList())))
.AddAttributeLists(forwardedFieldAttributes);

declarations.Add(fieldDeclaration);
}

// Prepares the argument to pass the underlying method to invoke
using ImmutableArrayBuilder<ArgumentSyntax> commandCreationArguments = ImmutableArrayBuilder<ArgumentSyntax>.Rent();
Expand Down Expand Up @@ -337,35 +345,44 @@ public static ImmutableArray<MemberDeclarationSyntax> GetSyntax(CommandInfo comm
ArrowExpressionClause(
AssignmentExpression(
SyntaxKind.CoalesceAssignmentExpression,
IdentifierName(commandInfo.FieldName),
commandInfo.FieldName is not null ? IdentifierName(commandInfo.FieldName) : IdentifierName("field"),
ObjectCreationExpression(IdentifierName(commandClassTypeName))
.AddArgumentListArguments(commandCreationArguments.ToArray()))))
.WithSemicolonToken(Token(SyntaxKind.SemicolonToken));

declarations.Add(propertyDeclaration);

// Conditionally declare the additional members for the cancel commands
if (commandInfo.IncludeCancelCommand)
{
// Prepare all necessary member and type names
string cancelCommandFieldName = $"{commandInfo.FieldName.Substring(0, commandInfo.FieldName.Length - "Command".Length)}CancelCommand";
string? cancelCommandFieldName = commandInfo.FieldName is not null ? $"{commandInfo.FieldName.Substring(0, commandInfo.FieldName.Length - "Command".Length)}CancelCommand" : null;
string cancelCommandPropertyName = $"{commandInfo.PropertyName.Substring(0, commandInfo.PropertyName.Length - "Command".Length)}CancelCommand";

// Construct the generated field for the cancel command as follows:
//
// /// <summary>The backing field for <see cref="<COMMAND_PROPERTY_NAME>"/></summary>
// [global::System.CodeDom.Compiler.GeneratedCode("...", "...")]
// private global::System.Windows.Input.ICommand? <CANCEL_COMMAND_FIELD_NAME>;
FieldDeclarationSyntax cancelCommandFieldDeclaration =
FieldDeclaration(
VariableDeclaration(NullableType(IdentifierName("global::System.Windows.Input.ICommand")))
.AddVariables(VariableDeclarator(Identifier(cancelCommandFieldName))))
.AddModifiers(Token(SyntaxKind.PrivateKeyword))
.AddAttributeLists(
AttributeList(SingletonSeparatedList(
Attribute(IdentifierName("global::System.CodeDom.Compiler.GeneratedCode"))
.AddArgumentListArguments(
AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(RelayCommandGenerator).FullName))),
AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(RelayCommandGenerator).Assembly.GetName().Version.ToString()))))))
.WithOpenBracketToken(Token(TriviaList(Comment($"/// <summary>The backing field for <see cref=\"{cancelCommandPropertyName}\"/>.</summary>")), SyntaxKind.OpenBracketToken, TriviaList())));
// Declare a backing field for the cancel command if needed.
// This is only needed if we can't use the field keyword for the main command, as otherwise the cancel command can just use its own field keyword.
if (cancelCommandFieldName is not null)
{
// Construct the generated field for the cancel command as follows:
//
// /// <summary>The backing field for <see cref="<COMMAND_PROPERTY_NAME>"/></summary>
// [global::System.CodeDom.Compiler.GeneratedCode("...", "...")]
// private global::System.Windows.Input.ICommand? <CANCEL_COMMAND_FIELD_NAME>;
FieldDeclarationSyntax cancelCommandFieldDeclaration =
FieldDeclaration(
VariableDeclaration(NullableType(IdentifierName("global::System.Windows.Input.ICommand")))
.AddVariables(VariableDeclarator(Identifier(cancelCommandFieldName))))
.AddModifiers(Token(SyntaxKind.PrivateKeyword))
.AddAttributeLists(
AttributeList(SingletonSeparatedList(
Attribute(IdentifierName("global::System.CodeDom.Compiler.GeneratedCode"))
.AddArgumentListArguments(
AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(RelayCommandGenerator).FullName))),
AttributeArgument(LiteralExpression(SyntaxKind.StringLiteralExpression, Literal(typeof(RelayCommandGenerator).Assembly.GetName().Version.ToString()))))))
.WithOpenBracketToken(Token(TriviaList(Comment($"/// <summary>The backing field for <see cref=\"{cancelCommandPropertyName}\"/>.</summary>")), SyntaxKind.OpenBracketToken, TriviaList())));

declarations.Add(cancelCommandFieldDeclaration);
}

// Construct the generated property as follows (the explicit delegate cast is needed to avoid overload resolution conflicts):
//
Expand Down Expand Up @@ -393,7 +410,7 @@ public static ImmutableArray<MemberDeclarationSyntax> GetSyntax(CommandInfo comm
ArrowExpressionClause(
AssignmentExpression(
SyntaxKind.CoalesceAssignmentExpression,
IdentifierName(cancelCommandFieldName),
cancelCommandFieldName is not null ? IdentifierName(cancelCommandFieldName) : IdentifierName("field"),
InvocationExpression(
MemberAccessExpression(
SyntaxKind.SimpleMemberAccessExpression,
Expand All @@ -402,10 +419,11 @@ public static ImmutableArray<MemberDeclarationSyntax> GetSyntax(CommandInfo comm
.AddArgumentListArguments(Argument(IdentifierName(commandInfo.PropertyName))))))
.WithSemicolonToken(Token(SyntaxKind.SemicolonToken));

return ImmutableArray.Create<MemberDeclarationSyntax>(fieldDeclaration, propertyDeclaration, cancelCommandFieldDeclaration, cancelCommandPropertyDeclaration);
declarations.Add(cancelCommandPropertyDeclaration);

}

return ImmutableArray.Create<MemberDeclarationSyntax>(fieldDeclaration, propertyDeclaration);
return declarations.ToImmutable();
}

/// <summary>
Expand Down Expand Up @@ -474,8 +492,9 @@ private static bool IsCommandDefinitionUnique(IMethodSymbol methodSymbol, in Imm
/// Get the generated field and property names for the input method.
/// </summary>
/// <param name="methodSymbol">The input <see cref="IMethodSymbol"/> instance to process.</param>
/// <param name="compilation">The compilation info, used to determine language version.</param>
/// <returns>The generated field and property names for <paramref name="methodSymbol"/>.</returns>
public static (string FieldName, string PropertyName) GetGeneratedFieldAndPropertyNames(IMethodSymbol methodSymbol)
public static (string? FieldName, string PropertyName) GetGeneratedFieldAndPropertyNames(IMethodSymbol methodSymbol, Compilation? compilation = null)
{
string propertyName = methodSymbol.Name;

Expand All @@ -498,6 +517,24 @@ public static (string FieldName, string PropertyName) GetGeneratedFieldAndProper

propertyName += "Command";

if (compilation is not null)
{
// We can use the field keyword as the generated field name if the language version is C# 14 or greater, or if it's C# 13 and the preview features are enabled.
// In this case, there is no need to generate a backing field, as the property itself will be auto-generated with an underlying field.
bool useFieldKeyword = false;

#if ROSLYN_5_0_0_OR_GREATER
useFieldKeyword = compilation.HasLanguageVersionAtLeastEqualTo(LanguageVersion.CSharp14);
#elif ROSLYN_4_12_0_OR_GREATER
useFieldKeyword = compilation.IsLanguageVersionPreview();
#endif

if (useFieldKeyword)
{
return (null, propertyName);
}
}

char firstCharacter = propertyName[0];
char loweredFirstCharacter = char.ToLower(firstCharacter, CultureInfo.InvariantCulture);

Expand Down
2 changes: 2 additions & 0 deletions tests/CommunityToolkit.Mvvm.UnitTests/Test_ObservablePropertyAttribute.cs
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Expand Up @@ -1003,6 +1003,7 @@ public void Test_ObservableProperty_WithExplicitAttributeForProperty()
Assert.AreEqual((Animal)67, testAttribute2.Animal);
}

#if !ROSLYN_4_12_0_OR_GREATER
// See https://github.com/CommunityToolkit/dotnet/issues/446
[TestMethod]
public void Test_ObservableProperty_CommandNamesThatCantBeLowered()
Expand All @@ -1021,6 +1022,7 @@ public void Test_ObservableProperty_CommandNamesThatCantBeLowered()

Assert.AreSame(model.c中文Command, fieldInfo?.GetValue(model));
}
#endif

// See https://github.com/CommunityToolkit/dotnet/issues/375
[TestMethod]
Expand Down
12 changes: 11 additions & 1 deletion tests/CommunityToolkit.Mvvm.UnitTests/Test_RelayCommandAttribute.cs
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Expand Up @@ -571,6 +571,7 @@ public void Test_RelayCommandAttribute_CanExecuteWithNullabilityAnnotations()
[TestMethod]
public void Test_RelayCommandAttribute_WithExplicitAttributesForFieldAndProperty()
{
#if !ROSLYN_4_12_0_OR_GREATER
FieldInfo fooField = typeof(MyViewModelWithExplicitFieldAndPropertyAttributes).GetField("fooCommand", BindingFlags.Instance | BindingFlags.NonPublic)!;

Assert.IsNotNull(fooField.GetCustomAttribute<RequiredAttribute>());
Expand All @@ -579,6 +580,7 @@ public void Test_RelayCommandAttribute_WithExplicitAttributesForFieldAndProperty
Assert.IsNotNull(fooField.GetCustomAttribute<MaxLengthAttribute>());
Assert.AreEqual(100, fooField.GetCustomAttribute<MaxLengthAttribute>()!.Length);

#endif
PropertyInfo fooProperty = typeof(MyViewModelWithExplicitFieldAndPropertyAttributes).GetProperty("FooCommand")!;

Assert.IsNotNull(fooProperty.GetCustomAttribute<RequiredAttribute>());
Expand Down Expand Up @@ -618,17 +620,21 @@ static void ValidateTestAttribute(TestValidationAttribute testAttribute)
Assert.AreEqual(Test_ObservablePropertyAttribute.Animal.Llama, testAttribute.Animal);
}

#if !ROSLYN_4_12_0_OR_GREATER
FieldInfo fooBarField = typeof(MyViewModelWithExplicitFieldAndPropertyAttributes).GetField("fooBarCommand", BindingFlags.Instance | BindingFlags.NonPublic)!;

ValidateTestAttribute(fooBarField.GetCustomAttribute<TestValidationAttribute>()!);
#endif

PropertyInfo fooBarProperty = typeof(MyViewModelWithExplicitFieldAndPropertyAttributes).GetProperty("FooBarCommand")!;

ValidateTestAttribute(fooBarProperty.GetCustomAttribute<TestValidationAttribute>()!);

#if !ROSLYN_4_12_0_OR_GREATER
FieldInfo barBazField = typeof(MyViewModelWithExplicitFieldAndPropertyAttributes).GetField("barBazCommand", BindingFlags.Instance | BindingFlags.NonPublic)!;

Assert.IsNotNull(barBazField.GetCustomAttribute<Test_ObservablePropertyAttribute.TestAttribute>());
#endif

PropertyInfo barBazCommand = typeof(MyViewModelWithExplicitFieldAndPropertyAttributes).GetProperty("BarBazCommand")!;

Expand Down Expand Up @@ -670,23 +676,27 @@ public void Test_RelayCommandAttribute_WithPartialCommandMethodDefinitions()
_ = Assert.IsInstanceOfType<RelayCommand>(model.BazCommand);
_ = Assert.IsInstanceOfType<AsyncRelayCommand>(model.FooBarCommand);

#if !ROSLYN_4_12_0_OR_GREATER
FieldInfo bazField = typeof(ModelWithPartialCommandMethods).GetField("bazCommand", BindingFlags.Instance | BindingFlags.NonPublic)!;

Assert.IsNotNull(bazField.GetCustomAttribute<RequiredAttribute>());
Assert.IsNotNull(bazField.GetCustomAttribute<MinLengthAttribute>());
Assert.AreEqual(1, bazField.GetCustomAttribute<MinLengthAttribute>()!.Length);
#endif

PropertyInfo bazProperty = typeof(ModelWithPartialCommandMethods).GetProperty("BazCommand")!;

Assert.IsNotNull(bazProperty.GetCustomAttribute<MinLengthAttribute>());
Assert.AreEqual(2, bazProperty.GetCustomAttribute<MinLengthAttribute>()!.Length);
Assert.IsNotNull(bazProperty.GetCustomAttribute<XmlIgnoreAttribute>());

#if !ROSLYN_4_12_0_OR_GREATER
FieldInfo fooBarField = typeof(ModelWithPartialCommandMethods).GetField("fooBarCommand", BindingFlags.Instance | BindingFlags.NonPublic)!;

Assert.IsNotNull(fooBarField.GetCustomAttribute<RequiredAttribute>());
Assert.IsNotNull(fooBarField.GetCustomAttribute<MinLengthAttribute>());
Assert.AreEqual(1, fooBarField.GetCustomAttribute<MinLengthAttribute>()!.Length);
Assert.AreEqual(1, fooBarField.GetCustomAttribute<MinLengthAttribute>()!.Length);
#endif

PropertyInfo fooBarProperty = typeof(ModelWithPartialCommandMethods).GetProperty("FooBarCommand")!;

Expand Down
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